A method is proposed for calculating the dimension distribution of nanocrystalline elements of the lamellar and fibrillar morphologies of a polymer. Calorimetric data were used to calculate the distribution of the longitudinal size of these elements in lamellae and microfibrils of ultrahigh molecular weight polyethylene. The calculation results are consistent with the data obtained by the X-ray method. V. M. Egorov1, A. K. Borisov1, V. A. Marikhin1, L. P. Myasnikova1, S. A. Gureva1, E. M. Ivan’kova2 1 Ioffe Institute, 26 Polytechnicheskaya, St. Petersburg 194021, Russia 2 Institute of Macromolecular Compounds, 31 Bolshoy pr., St. Petersburg 199004, Russia

A method for calculating the size distribution of nanocrystalline elements of the polymer structure is proposed. The longitudinal size distribution (thickness) of ultrahigh molecular weight polyethylene lamellae was calculated from calorimetric data. The results of calculating the maximum values of the distribution are consistent with the known data obtained by other methods.

In order to clarify the possibility of sintering reactor powders of ultra-high molecular weight polyethylene under pressure at a temperature higher than its equilibrium melting point at atmospheric pressure (T0m) without catastrophic changes in the internal structure of particles, a comparative WAXS analysis was carried out of the samples sintered below (T T0m) this temperature and cooled under different conditions. A multifunctional structural analysis of the X-ray scattering curves recorded in the Bragg-Brentano mode on a 2D Phaser Bruker diffractometer from UHMWPE reactor powders sintered under different conditions was carried out, and the crystallite sizes were calculated. It was found that an increase in the sintering temperature above T0m does not significantly change the crystal structure of the polymer, and the precursors produced can be used for further orientational hardening.

Regularities of statistical distributions of a complex of mechanical properties, including the module of elasticity (E), strength () and strain at break (b), high-strength industrial oriented polypropylene (PP) fibers have been analyzed using the Weibull and Gauss models based on large a wide array of measurements (50 identical samples in each series). The values of the statistical Weibull modulus (m) - a parameter characterizing the scatter of the measured values of the data arrays of E,  and b – have been estimated for the PP samples of two types: single fibers (monofilaments) and multifilament fibers consisting from several hundred single fibers. For the PP multifilament fibers, a more correct description of the distributions of E,  and b has been received both in the framework of the normal distribution (Gaussian distribution) and in the framework of the Weibull distribution in comparison with the description of such distributions for the PP monofilaments. The influence of the polymer chain conformation on the regularities of the statistical distributions of E,  and b for the high-strength oriented polymeric materials with different chemical chain structures and the correctness of their descriptions in the framework of the Gauss and Weibull models have been analyzed. For this purpose, the values of m calculated in this work for PP with a helical chain conformation have been compared with the values of m determined by us earlier for ultra-high molecular weight polyethylene and polyamide-6 with the chain conformations in the form of an in-plane trans-zigzag.

The patterns of the statistical distributions of tensile strength of high-strength ultraoriented mono-and multifilament fibers, consisting of several hundred single fibers of ultra-high-molecular-weight polyethylene (UHMWPE), have been analyzed using the Weibull and Gaussian models by considering a large number of measurements (50 identical samples in each series). It has been shown that the strength distribution of the multifilament UHMWPE fibers can be described both within the normal Gaussian distribution and the standard Weibull distribution function. At the same time, the strength distribution of the UHMWPE monofilaments oriented to a final draw ratio of 120 is not subject to the normal distribution. The reasons for the revealed differences in the types of the statistical strength distributions of the mono- and multifilaments of high-strength UHMWPE during fracture are discussed.

Annotation The X-ray analysis of a virgin particle taken directly from the synthesis products of an ultra-high molecular weight polyethylene (UHMWPE) and not subjected to any external stresses was carried out using nanofocus beamline ID13 European Synchrotron Radiation Facility (ESRF, Grenoble,France). In the X-ray diffraction curves obtained by scanning an arbitrarily selected portion of a particle with a size of (100 x 20) μm2 by a microbeam (0.3 x 0.3) μm2 with a step of 2 μm horizontally and 0.5 μm vertically, along with reflections from the orthorhombic phase, reflexes from the metastable monoclinic phase were observed. It is believed that the cause of its occurrence may be stresses that develop during specific structure formation in slurry synthesis and persist when cooled to room temperature and the solvent evaporates. The possibility of localization of the monoclinic phase in various morphological formations is discussed.

AbstractThe influence of the gauge length l _0 of a sample on the modulus E of ultraoriented film filaments of ultra-high-molecular-weight polyethylene (UHMWPE) has been elucidated. The filament samples are obtained by a multistage orientation drawing on a contact heater with achieving extremely high draw ratios as large as λ = 120. Precursors were xerogels prepared by the drying of 1.5% UHMWPE gel solutions in decalin. A noticeable gain in “methodical” quantity E from 100 to 230 GPa at l _0 increasing from 10 to 80 mm with a damping behavior has been established. The E ( l _0) dependence is shown to be described via the empirical equation that allows the E value to be predicted as a function of l _0. According to the prediction, a saturation of the true value E with a yield to a plateau at E = 242 GPa occurs at l _0 = 200 mm.

The kinetics of the structural first order phase transition in the tetracosane С24Н50 monodisperse samples is studied with the help of FTIR spectroscopy. The temperature dependencies of the frequency and intensity of rocking (ν~ 720 cm-1) and bending (ν~ 1470 cm-1) vibrations of СН2-groupes in the methylene trans-sequences in the crystalline cores of the elementary lamellae are investigated. It is shown that the first order solid phase transition is developing on a heterogeneous mechanism in the narrow temperature interval (T~ 2 K) according to the theory of the diffused first order phase transitions and is due to the crystalline cell symmetry change.

A statistical analysis of the distributions of Young's modulus Е and strain at break b of the commercial oriented fibers of polyamide-6 has been carried out in the frameworks of the models of Gauss and Weibull. The duality of the statistical distributions of Е and b revealed earlier for the strength of polyamide-6 has been confirmed. It consists in the validity of the description of the experimental data by using both the normal Gaussian distribution and the standard Weibull distribution function.

AbstractWe analyze heat effects associated with the solid-state phase transition in ultrahigh molecular weight polyethylene from the unstable monoclinic phase into thermodynamically stable orthorhombic phase. The model proposed here for the structure of supramolecular formations of monoclinic phase does not contradict to earlier X-ray diffraction data for this polymer.

With the help of small angle X-ray diffraction using synchrotron X-ray beamline"Belok" in NRC «Kurchatov Institute» was shown that the first order sold phase transition in the tetracosane C24H50 develops by a heterogeneous mechanism in a very narrow thermal interval (delta ≈0,1K ) in accordance with the theory of diffuse phase transition. The work was financially supported by the Presidium RAN Program №32 "Nanostructures: physics, chemistry, biology, basics of technology" and Russian Foundation of Basic Research (project 16-03-00493А) using beamline "Belok" in NRC

AbstractStatistical analysis of distribution of the tensile strength of commercial oriented polyamide-6 (PA-6) fibers has been performed in the framework of the Gaussian and Weibull models using a large data array of the results of measurements for a large number (50) of identical samples. Using the example of PA-6, the dualism of strength distribution in oriented high-strength polymers is demonstrated for the first time, which consists in the validity of both the normal Gaussian distribution (characteristic of viscoelastic and plastic materials) and the Weibull distribution (characteristic of brittle materials).

AbstractUsing powerful synchrotron X-ray radiation of the beamline “Belok” operated by the National Research Center “Kurchatov Institute,” we perform X-ray diffraction (XRD) study of an intact, virgin (not subjected to any external mechanical loads) particle isolated from reactor powder of ultrahigh molecular weight polyethylene. Along with the peaks originating from the orthorhombic phase, we detect the peaks characteristic of the monoclinic phase that is stable only under mechanical stress, suggesting that the mechanical stress that leads to the formation of the monoclinic phase and persists at room temperature develops during the polymer synthesis. The monoclinic phase gradually disappears when the particle is heated stepwise in increments of 5 K, and its peaks become undetectable when the temperature reaches 340 K. We contrast the results obtained for the phase composition of the virgin particle to those for a tablet prepared by compaction of the same reactor powder at room temperature. XRD analyses of the tablet were performed on D2 Phaser (Bruker) instrument. The monoclinic phase that originates during the polymer synthesis and the one that forms in the tablet during compaction have different parameters. We discuss the mechanisms by which these two different monoclinic phases originate during the processes involved.

Методом дифференциальной сканирующей калориметрии исследованы фазовые переходы в нормальных алканах: трикозане (C23H48), тетракозане (C24H50) и пентакозане (C25H52). Устранение методических погрешностей позволило получить истинные значения термодинамических параметров фазовых переходов и выявить их природу. Проведен сравнительный анализ скачков теплоемкости на основе теории размытых фазовых переходов первого рода. Работа выполнена при финансовой поддержке РФФИ (код проекта N 16-03-00493). DOI: 10.21883/FTT.2017.10.44978.095

Методом ИК-Фурье спектроскопии изучены структурные изменения в кристаллических сердечниках ламелей тридекановой кислоты СН3(СН2)11СООН при нагревании от T1=13.5oC до T2>Tm=41.6oC. Анализировалось поведение полос маятниковых (область 720 cm-1) и деформационных (область 1470 cm-1) колебаний СН2-групп в метиленовых отрезках тридекановой кислоты. Показано, что в области фазового перехода I рода (Ts-s~36oC) в узком температурном интервале (Delta T1≤1 K) происходит постепенная трансформация исходной триклинной субъячейки в гексагональную субъячейку. Рассмотрен механизм этого перехода с позиции теории диффузионных фазовых переходов I рода. Работа выполнена при финансовой поддержке Российского фонда фундаментальных исследований (код проекта 16-03-00493). DOI: 10.21883/FTT.2017.02.44056.285

С целью выявления особенностей структуры реакторных порошков сверхвысокомолекулярного полимера в зависимости от каталитической системы, на которой проводится синтез, осуществлено сравнительное исследование серии лабораторных и коммерческого порошков сверхвысокомолекулярного ПЭ, синтезированных на разных катализаторах в суспензионном процессе в различных условиях. Использован целый комплекс современных физических методик, таких как просвечивающая и сканирующая электронная микроскопия, рентгеноструктурный анализ, спектроскопия комбинационного рассеяния, дифференциальная сканирующая калориметрия, ядерный магнитный резонанс и термолюминесценция. Найдено, что все насцентные частицы имеют сложную иерархическую структуру. Элементарной структурной единицей во всех реакторных порошках являются кристаллические ламели, размер и взаимная ориентация которых определяются типом каталитической системы. При синтезе на нанесенных катализаторах характер образующейся структуры зависит от свойств подложки. При разрушении подложки во время синтеза образуются фибриллы. Коллоидные размеры частиц катализатора обусловливают более однородную ламелярную структуру реакторных порошков. Дана оценка конформационного состава сегментов молекул в межламелярных областях реакторных порошков.